Butter a 12 x 18 inch jelly roll pan and line the bottom with a sheet of parchment or waxed paper.
In a large mixer bowl, beat 1 cup butter with the sugar until soft and light. Add the eggs one at a time, beating well between each addition. Beat in the vanilla.
Sift together 2 cups of flour and baking powder and stir into the batter in three additions, alternating with the yolks and milk, beginning and ending with the flour. Spread the batter evenly in the prepared pan. Scatter the blueberries evenly over the batter, pressing them in gently.
Mix the remaining 1/2 cup of flour with brown sugar, cinnamon and nutmeg in a bowl. Melt the remaining 3/4 cup of butter and stir it in evenly. Rub the mixture to coarse crumbs by hand. Scatter the crumbs over the berries as evenly as possible.
Bake the crumb cake about 40 minutes at 350°F until batter is firm and crumbs are golden brown. Cool the cake in the pan on a rack. Cut into 3 inch squares. Remove the squares from the pan to a platter.